The Cold War began in 1945 due to ideological differences between Western democracies led by the United States and the Soviet-controlled Eastern Bloc. As the postwar order was negotiated, disagreements arose over the rebuilding of Europe and control of Poland and Germany. The Cold War intensified as the Soviet Union expanded its influence over Eastern Europe and China, countered by the US Truman Doctrine, Marshall Plan, NATO alliance, and NSC-68 policy of containment. The conflict escalated further in the early 1950s with the outbreak of the Korean War and fears in the US of communist subversion and espionage.